uses crt;
var
i:integer;
a,b,c,d,x1,x2,p1,p2,t,y,u:real;
r:real;
begin
clrscr;
write('a= ');
read(a);
write('b= ');
read(b);
write('c= ');
read©;
If (a=0) then
begin
If (b=0) then
begin
If (c=0) then
writeln('infinitnoye mnojestvo')
else
writeln('korney net');
end
else begin
x1:=-c/b;
writeln('koren ',x1:4:4);
p1:=a*x1*x1+b*x1 + c;
writeln('proverca: ax1^2+bx1+c= ',p1);
end;
end
else
begin
d:=(sqr(b)-4*a*c);
t:=sqrt(D);
If (d<0) then
writeln('real korney net')
else
begin
writeln;
writeln;
x1:=(- b - t ) / (2*a);
x2:=(- b + t ) / (2*a);
writeln('koren1= ',x1);
writeln('koren2= ',x2);
p1:=a*x1*x1 + b*x1 + c;
writeln('proverca1: ax1^2+bx1+c= ',p1);
p2:=a*x2*x2 + b*x2 + c;
writeln('proverca2: ax2^2+bx2+c= ',p2);
end;
end;
readln;
readln;
end. 

{$n+}
uses crt;
const
  eps = 10E-9;

var
i:integer;
a,b,c,d,x1,x2,p1,p2,t,y,u:double;
r:real;
begin
  clrscr;
  write('a= '); readln( a );
  write('b= '); readln( b );
  write('c= '); readln( c );
  
  if abs(a) < eps then begin
    if abs(b) < eps then begin
      if abs© < eps then
        writeln('infinitnoye mnojestvo')
      else
        writeln('korney net');
    end
    else begin
      x1:=-c/b;
      writeln('koren ',x1:4:4);
      p1:=a*x1*x1+b*x1 + c;
      writeln('proverca: ax1^2+bx1+c= ',p1);
    end;
  end
  else begin
    d:=(sqr(b)-4*a*c);
    t:=sqrt(D);
    If (d<0) then writeln('real korney net')
    else begin
      writeln;
      writeln;
      x1:=(- b - t ) / (2*a);
      x2:=(- b + t ) / (2*a);
      writeln('koren1= ',x1);
      writeln('koren2= ',x2);
      p1:=a*x1*x1 + b*x1 + c;
      writeln('proverca1: ax1^2+bx1+c= ',p1);
      p2:=a*x2*x2 + b*x2 + c;
      writeln('proverca2: ax2^2+bx2+c= ',p2);
    end;
  end;
  readln;
  readln;
end.

var
  ...
  a,b,c,d,x1,x2,p1,p2,t,y,u:real;
  ...
  If (a=0) then ... { вещественное A? Сравниваем через "="? Некорректно... }
  If (b=0) then ... { аналогично }
  If (c=0) then ...

      p1:=a*x1*x1 + b*x1 + c;
      writeln('proverca1: ax1^2+bx1+c= ',p1:10:7);
      p2:=a*x2*x2 + b*x2 + c;
      writeln('proverca2: ax2^2+bx2+c= ',p2:10:7);